Scientists have discovered a new planet with the mass of Earth,
orbiting its star at the same distance that we orbit our sun. The planet
is likely far too cold to be habitable for life as we know it, however,
because its star is so faint. But the discovery adds to scientists'
understanding of the types of planetary systems that exist beyond our
own.
"This 'iceball' planet is the lowest-mass planet ever found through
microlensing," said Yossi Shvartzvald, a NASA postdoctoral fellow based
at NASA's Jet Propulsion Laboratory, Pasadena, California, and lead
author of a study published in the Astrophysical Journal Letters.
Microlensing is a technique that facilitates the discovery of distant
objects by using background stars as flashlights. When a star crosses
precisely in front of a bright star in the background, the gravity of
the foreground star focuses the light of the background star, making it
appear brighter. A planet orbiting the foreground object may cause an
additional blip in the star's brightness. In this case, the blip only
lasted a few hours. This technique has found the most distant known
exoplanets from Earth, and can detect low-mass planets that are
substantially farther from their stars than Earth is from our sun.
The newly discovered planet, called OGLE-2016-BLG-1195Lb, aids
scientists in their quest to figure out the distribution of planets in
our galaxy. An open question is whether there is a difference in the
frequency of planets in the Milky Way's central bulge compared to its
disk, the pancake-like region surrounding the bulge.
OGLE-2016-BLG-1195Lb is located in the disk, as are two planets
previously detected through microlensing by NASA's Spitzer Space
Telescope.
"Although we only have a handful of planetary systems with
well-determined distances that are this far outside our solar system,
the lack of Spitzer detections in the bulge suggests that planets may be
less common toward the center of our galaxy than in the disk," said
Geoff Bryden, astronomer at JPL and co-author of the study.
For the new study, researchers were alerted to the initial
microlensing event by the ground-based Optical Gravitational Lensing
Experiment (OGLE) survey, managed by the University of Warsaw in Poland.
Study authors used the Korea Microlensing Telescope Network (KMTNet),
operated by the Korea Astronomy and Space Science Institute, and
Spitzer, to track the event from Earth and space.
KMTNet consists of three wide-field telescopes: one in Chile, one in
Australia, and one in South Africa. When scientists from the Spitzer
team received the OGLE alert, they realized the potential for a
planetary discovery. The microlensing event alert was only a couple of
hours before Spitzer's targets for the week were to be finalized, but it
made the cut.
With both KMTNet and Spitzer observing the event, scientists had two
vantage points from which to study the objects involved, as though two
eyes separated by a great distance were viewing it. Having data from
these two perspectives allowed them to detect the planet with KMTNet and
calculate the mass of the star and the planet using Spitzer data.
"We are able to know details about this planet because of the synergy
between KMTNet and Spitzer," said Andrew Gould, professor emeritus of
astronomy at Ohio State University, Columbus, and study co-author.
Although OGLE-2016-BLG-1195Lb is about the same mass as Earth, and
the same distance from its host star as our planet is from our sun, the
similarities may end there.
OGLE-2016-BLG-1195Lb is nearly 13,000 light-years away and orbits a
star so small, scientists aren't sure if it's a star at all. It could be
a brown dwarf, a star-like object whose core is not hot enough to
generate energy through nuclear fusion. This particular star is only 7.8
percent the mass of our sun, right on the border between being a star
and not.
Alternatively, it could be an ultra-cool dwarf star much like
TRAPPIST-1, which Spitzer and ground-based telescopes recently revealed
to host seven Earth-size planets. Those seven planets all huddle closely
around TRAPPIST-1, even closer than Mercury orbits our sun, and they
all have potential for liquid water. But OGLE-2016-BLG-1195Lb, at the
sun-Earth distance from a very faint star, would be extremely cold --
likely even colder than Pluto is in our own solar system, such that any
surface water would be frozen. A planet would need to orbit much closer
to the tiny, faint star to receive enough light to maintain liquid water
on its surface.
Ground-based telescopes available today are not able to find smaller
planets than this one using the microlensing method. A highly sensitive
space telescope would be needed to spot smaller bodies in microlensing
events. NASA's upcoming Wide Field Infrared Survey Telescope (WFIRST),
planned for launch in the mid-2020s, will have this capability.
"One of the problems with estimating how many planets like this are
out there is that we have reached the lower limit of planet masses that
we can currently detect with microlensing," Shvartzvald said. "WFIRST
will be able to change that."
JPL manages the Spitzer Space Telescope mission for NASA's Science
Mission Directorate, Washington. Science operations are conducted at the
Spitzer Science Center at Caltech in Pasadena, California. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at the Infrared Science Archive
housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA. For more information about Spitzer, visit: http://spitzer.caltech.edu - http://www.nasa.gov/spitzer
News Media Contact
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov
